Pager service providers transmit messages through radio communication centers (RCC's) to selective call receivers within a specified geographic calling area. Generally, the service providers maintain transmitters at various locations throughout the calling area to insure that messages are effectively transmitted and received by a selective call receiver anywhere in the area. However, each of the various transmitters do not transmit the message at exactly the same time. As a result, an identical or "duplicate" message may be received by the selective call receiver only moments after an original message is received. The duplicate message can become an annoyance and in certain instances can confuse service subscribers. Therefore, in order to eliminate duplicate messages, one-way selective call receivers incorporate a sequential lockout which deletes duplicate messages that are received within a pre-specified time period. As a result, subscribers are not alerted to duplicate messages and thus the annoyance and confusion is eliminated.
Certain RCC's also provide two-way service for subscribers that possess two-way pagers. In addition to receiving messages, two-way pagers are able to respond to received messages when a response enable flag is transmitted with a message. In particular, when a response is enabled, two-way pager users can respond to the received message with a response that is selected by the user from a set of responses or with one of a preprogrammed set of responses.
The ability to respond necessitates message tracking in the pager software such that both the pager and the paging system can identify which message is being responded to. Accordingly, a unique tracking identifier ("signature") is transmitted with each message. Generally, identical messages with different tracking identifiers correspond to messages sent by different sources who are both expecting a reply to their page. However, since the number of possible tracking identifiers is finite, tracking identifiers wrap and repeat. This permits a situation where both a message and tracking identifier may be identical to that of an existing message and the source is not the same person. In this situation, if duplicate messages were distinguished solely on the basis of the message content and the tracking identifier, the sequential lockout method would delete the new message which in turn would disable the subscriber's ability to respond to the new page if a response were enabled for the new page. Even though the message and tracking identifier are identical the response flag could be enabled on the new message but disabled on the original. Accordingly, if the new message is deleted so would the ability to respond. On the other hand, storing an entire duplicate message in a two-way pager's memory in order to maintain the ability to respond takes up valuable memory space and is generally an inefficient means for processing duplicate messages. Therefore, there is a present need for an improved method for processing duplicate messages that maintains the optimum ability to respond to both original and duplicate messages and saves message memory in a two-way paging device by deleting select portions of original and duplicate messages.